1. Technical Field
The present invention relates to telephone switching systems and, more particularly, to a system which receives requests for placing long distance telephone calls and responds by establishing least cost routing connection in setting up the calls.
2. Discussion of the Prior Art
Numerous companies are presently in the long distance telephone service resale business wherein customers are offerred low cost long distance rates. Access to such systems is generally achieved by dialing a local telephone number. Upon receiving an access acknowledgement signal, the customer then dials in his or her user code followed by the telephone number of the party being called. The system is able to take advantage of high volume rates, low cost, transmission links, etc., in order to provide low billing rates.
It is desirable that such a system be capable of determining the least cost routing for a long distance call at any given time in order to minimize the system owner's costs. This desirable feature has resulted in development of least cost routing telephone switches which must include the following:
(1) A group of ports for connection to incoming telephone lines, from which requests for calls are received;
(2) A group of ports for connection to outgoing telephone lines, on which calls are placed to destination;
(3) A set of DTMF decoders to receive information from the requesting user;
(4) A set of DTMF encoders to dial outgoing telephone numbers;
(5) A set of ready tone generators to inform the user that the system is ready to receive information;
(6) A set of dial tone detectors to determine when outgoing lines are ready to receive dialing information;
(7) A means to connect incoming ports, DTMF encoders, and dial tone detectors to outgoing ports, DTMF decoders, and ready tone generators (such as a crosspoint array); and
(8) A control structure to coordinate all activities, execute a least cost algorithm for assignment of outgoing lines, create billing and statistical records, and perform ancillary functions, such as line testing.
Conventional switch systems use a high-speed minicomputer or mainframe computer to perform the last function. This provides the one central control computer access to all hardware and responsibility for performing all activities of the entire switch in real time. These activities include line monitoring, crosspoint control, DTMF decoder and encoder allocation, and port control, in addition to algorithmic and recordkeeping functions. In effect, every single action taken in the system is directly controlled by the one computer (dual or triple computers used solely for reliability or diagnostic functions are used essentially as a single computer). The computer must be relatively fast in order to be able to perform all tasks in real time. Such a computer is expensive, thereby adding significantly to the system cost and the charges which must be passed on to the customer. In addition, even for the fastest of computers, undesirable delays are experienced in call handling, particularly during peak traffic time periods.